1. Field of the Invention
The present invention relates to a method for driving a touch panel device, and more particularly, to a method for driving a touch panel device that detects a double touch and prevents a detection error caused by a double touch by a stylus or a user's finger.
2. Description of the Related Art
In general, touch panel devices are considered computer peripherals that are installed on a display surface of display devices, such as cathode ray tube (CRT) devices, liquid crystal display (LCD) devices, field emission display (FED) devices, plasma display panel (PDP) devices, and electro-luminescence display (ELD) devices to eliminate uses of other input devices. By integrating touch panels with display devices, it is possible for a user to select desired information while watching an image displayed by the display device. For example, the user selects desired information by touching and applying pressure onto the touch panel where the information is displayed, and the touch panel detects a coordinate of such touch to determine the user's selection.
Touch panels may be classified based on the detection mechanism used therein. For example, there are analog resistive type, capacitive type, electromagnetic (EM) type, saw type and infrared type of touch panels. In particular, a capacitive type touch panel typically includes upper and lower transparent substrates bonded to each other with a predetermined space therebetween. Each of the upper and lower transparent substrates includes upper and lower electrodes formed thereon. Accordingly, if the surface of the upper transparent substrate is touched by an input means, such as a stylus or a user's finger, the upper electrode on the upper transparent substrate then electrically connects to the lower electrode formed on the lower transparent substrate. As a result, a variation in a voltage caused by a resistance change or a capacitance change at the touched point can be detected.
In addition, when the capacitive type touch panel is installed on an LCD device, a film having a transparent electrode typically is formed on the LCD panel with a voltage applied to each corner of the film, thereby generating an uniform electric field in the transparent electrode. Thus, when the surface of the LCD touch panel is touched by an input means, a voltage drop can be generated to additionally detect coordinates of the touched point.
FIG. 1 illustrates a schematic view of a method for driving a resistive type touch panel device according to the related art. In FIG. 1, the touch panel device includes a touch panel 10, a touch panel controller 30, and a system 40. In particular, the touch panel controller 30 drives the touch panel 10, detects a coordinate signal outputted from the touch panel 10, measures coordinates according to the outputted coordinate signal, and then outputs the measured value of the coordinates to the system 40. The system 40 then performs a command corresponding to the measured value of the coordinates.
In addition, the touch panel 10 includes an upper film 12 and a lower film 16 facing each other with a predetermined space therebetween. A first transparent conductive layer 14 is formed on a lower surface of the upper film 12, and a second transparent conductive layer 18 is formed on an upper surface of the lower film 16. The upper film 12 and the lower film 16 are bonded to each other in the circumference of a non-touch area thereof by an adhesive 22. Thus, the predetermined space between the upper and lower films 12 and 16 corresponds to a thickness of the adhesive 22. A plurality of dot spacers 20 are additionally formed in a touch area on the first transparent conductive layer 14 of the upper film 12 or the second transparent conductive layer 18 of the lower film 16 to maintain the predetermined space between the upper and lower films 12 and 16.
In general, the upper film 12 is formed of a transparent film such as a Polyethylene Terephtalate (PET) film, and the lower film 16 is formed of a transparent film, a glass substrate or a plastic substrate of the same material as the upper film 12. The first and second transparent conductive layers 14 and 18 are formed of one of Indium-Tin-Oxide (ITO), Indium-Zinc-Oxide (IZO) and Indium-Tin-Zinc-Oxide (ITZO).
Further, the touch panel 10 includes an X-electrode bar 15 and a Y-electrode bar 19. The X-electrode bar 15 includes two side bars, first and second X-electrode bars 15A and 15B, contacting two sides of the first transparent conductive layer along an X-axis direction, respectively, and applying a voltage to the first transparent conductive layer 14 along the X-axis direction. The first X-electrode bar 15A applies a driving voltage Vcc to form a current in the first transparent conductive layer 14 along the X-axis direction, and the second X-electrode bar 15B applies a ground voltage GND. The Y-electrode bar 19 also includes two side bars, first and second Y-electrode bars 19A and 19B, contacting two sides of the second transparent conductive layer 18 along a Y-axis direction, respectively, and applying a voltage to the second transparent conductive layer 18 along the Y-axis direction. The first Y-electrode 19A applies a driving voltage Vcc to form a current in the second transparent conductive layer 18 along the Y-axis direction, and the second Y-electrode bar 19B applies a ground voltage GND.
When a user touches the upper film 12 of the touch panel 10 with an input means, the first transparent conductive layer 14 then contacts the second transparent conductive layer 18, such that a resistance value varies at the touched point. Subsequently, the current or the voltage varies according to the varied resistance value, so that an X-axis coordinate signal is outputted through the second Y-electrode bar 19B, and a Y-axis coordinate signal is outputted through the second X-electrode bar 15B.
In particular, the touch panel 10 sequentially outputs the X-axis and Y-axis coordinate signals based on a control signal from the touch panel controller 30. The controller 30 selectively provides the driving voltage Vcc and the ground voltage GND to the first and second X-electrode bars 15A and 15B through a first switch 24 and a second switch 26, respectively, thereby controlling the touch panel 10 to output the X-axis coordinate signal through the second Y-electrode bar 19B. Subsequently, the touch panel controller selectively provides the driving voltage Vcc and the ground voltage GND to the first and second Y-electrode bars 19A and 19B through the first and second switches 24 and 26, respectively, thereby controlling the touch panel 10 to output the Y-axis coordinate signal through the second X-electrode bar 15B. The first switch 24 selectively provides the driving voltage Vcc to the first X-electrode bar 15A or the first Y-electrode bar 19A in response to a control signal CS outputted from the touch panel controller 30. Also, in response to the control signal, the second switch 26 selectively provides the ground voltage GND to the second X-electrode bar 15B or the second Y-electrode bar 19B or selectively outputs the voltage of the touched point from the touch panel to the touch panel controller 30.
The touch panel controller 30 includes an analog-digital converter (ADC) 32, a micom 34 and an interface 36. When the touch panel controller 30 receives the X-axis and Y-axis coordinate signals from the touch panel 10, the ADC 32 sequentially converts the X-axis and Y-axis coordinate signals to digital data. The micom 34 then detects the coordinate value by combining the X-axis and Y-axis coordinate data, and the interface 36 relays the coordinate value to the system 40. In addition, the micom 34 periodically generates the control signal CS.
The system 40 detects the coordinate value from the touch panel controller 30, and performs a command or an applied program corresponding to the coordinate value. Also, the system 40 provides a power source signal and a video data signal for a display (not shown) formed on a surface of the touch panel 10. Thus, the touch panel device detects the coordinate value touched by the pen or the user's finger, and then transmits the coordinate value to the system 40, such that the system 40 performs a command corresponding to the coordinate value.
FIG. 2 illustrates a cross-sectional view of a double touch on a touch panel. In FIG. 2, a double touch occurs when the upper film 12 unintentionally is touched with a pen and a user's hand at the same time or within a short time interval. When the pen and the user's hand touch the touch panel 10 at the same time, the touch panel 10 generates a coordinate signal corresponding to a middle point between the pen touch point PT and the hand touch point HT, instead of the pen touch point PT. Subsequently, the touch panel controller 30 and the system detect and process the coordinate signal for the middle point erroneously as the user's desired input.
Alternatively, when the user's hand unintentionally touches the upper film 12 shortly after the pen touching the upper film 12, the touch panel 10 generates a first coordinate signal for the pen touch point Pt, and then a second coordinate signal for a middle point between the pen touch point PT and the hand touch point HT. If both the first and second coordinate signals are generated within a unit time period, e.g., 3.4 ms, the touch panel controller detects the second coordinate signal as the user's desired input, because the touch panel 10 sequentially outputs the coordinate signals and the second coordinate signal is a later signal inputted to the touch panel controller 30. Thus, the touch panel controller 30 and the system erroneously process the coordinate signal for the middle point as the user's desired input. Thus, the performance of the related art method for driving touch panel has not been fully satisfactory.